The Combustion Process

The combustion in fired heaters takes place in the burner. The types of burners and how they function are not covered in detail in this section. The amount of heat released can be easily calculated for a gas when we know the composition of the fuel and the heating values of the various components. For liquid fuels, the heating values are obtained by a calorimeter test.
From these values and using the standard combustion equation, we can determine the composition of the flue gas. As an example, the combustion of methane could be stated :

CH4 + 2O2 --- > CO2 + 2H2O
Of course for fuel gases containing many more components and burning in air rather than pure oxygen, the equation gets more complicated. Therefore, a task that in itself is quite simple, becomes a burden to do by hand, but can be easily accomplished by a simple computer program. The heating values normally used in fired heater design are the LHV, lower heating values.
To try some calculations, click the button below to open another window to do some fuel combustion calculations:

The following Lower Heating Values(LHV) are used in this script:
ComponentBtu/lb ComponentBtu/lb ComponentBtu/lb
CH421,520 C2H620,432 C3H819,944
N-C4H1019,680 I-C4H1019,629 N-C5H1219,517
I-C5H1219,478 C6H1419,403 CO4,347
H251,623 N20 CO20
C14,093 S3,983 C2H420,295
C3H619,691 C4H819,496 C6H617,480
H2O0 O20 H2S6,545